> why hire a structural engineer? ...

   Structural engineers have the knowledge to determine the causes of the structural problems you are experiencing with your home or building and the best remedies for those problems. Except for architects, no other professional or craftsperson has that knowledge or license.

   Contractors know best how to implement the repairs but are not well-qualified to determine the cause or the best remedy. Also, they are often not in an impartial position, as they are selling the methods used by their company.